Regadenoson Vasodilation: Regadenoson is a selective A2A adenosine receptor agonist FDA released as a pharmacologic vasodilator in nuclear stress myocardial perfusion imaging (MPI). It has a higher affinity for A2A receptors than adenosine and is a more potent coronary vasodilator. Adenosine infusion is the gold standard for both invasive and non-invasive assessment of myocardial blood flow reserve, yet regadenoson with potentially greater coronary arterial vasodilation and a simple bolus injection is an ideal agent with which to study differences in CFR between different disease states. Limited data is published on the utility of regadenoson in invasive assessment of CFR and no data are published regarding the utility of this agent in assessing the hyperemic myocardial blood flow response with respect to cardiac MRI.